send mail to support@abhimanu.com mentioning your email id and mobileno registered with us! if details not recieved
Resend Opt after 60 Sec.
By Loging in you agree to Terms of Services and Privacy Policy
Claim your free MCQ
Please specify
Sorry for the inconvenience but we’re performing some maintenance at the moment. Website can be slow during this phase..
Please verify your mobile number
Login not allowed, Please logout from existing browser
Please update your name
Subscribe to Notifications
Stay updated with the latest Current affairs and other important updates regarding video Lectures, Test Schedules, live sessions etc..
Your Free user account at abhipedia has been created.
Remember, success is a journey, not a destination. Stay motivated and keep moving forward!
Refer & Earn
Enquire Now
My Abhipedia Earning
Kindly Login to view your earning
Support
India is perhaps the only country in the world where wide variation occurs in such a close proximity. Almost every type of climate prevails in India simultaneously. Places in the interior have continental climatic characteristics i.e. very hot, summers & cold dry winters. The coastal regions have equable climate due to the influence of the sea, namely land and sea breezes caused by the differential rate of heating and cooling of land and water. The southern part of the sub-continent remains hot throughout the year with a low annual range of temperature about 2o to 3oC, as it is closer to the equator. Due to altitude, places located on the high mountains of the North remain cold throughout the year.
Though the continent of Asia has varied climatic conditions, the general climate of the sub-continent is the Tropical Monsoon type. The climate of the subcontinent is greatly affected by the presence and influence of the Himalayas. The Tropic of Cancer 23-1/2oN passes through the centre of the country so the region north of the line should have had a temperate climate due to the fact that it never experiences vertical rays of the sun, but actually this is not so. The Himalayas present the bitterly cold winds of the north from entering the sub-continent & also moderate the temperatures south of the Himalayas; hence the northern part also has a tropical monsoon climate, giving the sub-continent a characteristic tropical monsoon climate. Himalayas also intercept the rain bearing South-West monsoon winds, causing torrential rain.
The word monsoon has been derived from the Arabic word ‘mausim’ which means seasonal reversal of the winds during the course of the year. This implies a rhythmic change in the direction of the winds and in the distribution of temperature & rainfall with the change of season.
No where else in the world is the monsoon climate so well marked as in the Indian sub-continent. This is due to the pressure system, which is well developed over the land & sea and due to the presence of a large land mass & water body. Differential heating & cooling of land & water is the chief cause of the tropical monsoon type of climate.
During the early periods, when only surface observations were available from stations on the land or from at sea, the bursting of the monsoon was explained as the diversion of south-east trades from the southern part of Indian Ocean towards the low pressure trough over North India. As the south-east trade winds cross the equator, they get deflected to south-west and reach Andaman Islands and Kerala coast. As these winds travel over vast ocean surface, they have high humidity and cause heavy rainfall.
Later, it was considered that the shifting of the Inter-Iropical Convergence zone (ITCZ) to the Northern Plains resulted in the formation of Equatorial Westerlies which blow towards the ITCZ. As the position and intensity of ITCZ vary, the intensity of the winds also varies. The tropical maritime air moving over India from the Indian Ocean advances as a front. With its arrival, the monsoon bursts bringing about a sudden change in weather. Heavy squally rain accompanied by thunder and lightning hearald the arrival of the monsoon. The numerous storms and the disturbances which cause rainfall in the monsson season are associated with oscillations of the ITCZ. This theory was originally elaborated by Flohn, a German meteorologist.
With systematic study of Upper Air Data for several years, it has become evident that the circulation in the lower layers of the atmosphere is only a part of the total circulation which takes place at different levels in the troposphere and stratosphere. A westerly jet stream is located south of the Himalayas at a height of about 12km. With the onset of summer, the westerly jet stream gets displaced to a position north of Tien Shah. This shift of the path of the jet stream, north of the Himalayas enables movement of monsoon air masses over India. In the place of the westerly jet stream an easterly jet stream is seen in upper air over Peninsular India. The northward and southward oscillation of this jet stream influences the weather in the monsoon season including the periods of break.
Besides the jet streams in upper air, the progress of the monsoon is dependent on the circulation of air over the Tibetan plateau. Tibetan plateau is unusually hot during summer compared to its latitude and altitude. The hot air over Tibet rises and flows towards the Equator at higher levels and sinks over the Indian Ocean. This air moves as the monsoon current over India in the lower layers of the atmosphere. This air current, also known as equatorial westerlies, blows as the south-west monsoon. The intensity of the monsoon depends on upper air circulation from Tibet.
The mechanism of the Indian monsoon is sought to be explained by the shifting of the Inter-Tropical Convergence, the northward movement of westerly jet stream and its replacement by easterly jet stream and the upper air circulation over Tibet. The world Meterological Organisation conducted Monsoon Experiment (MONEX) over the Arabian Sea and the Bay of Bengal to unravel the mysteries about the monsoon. In spite of all these attempts, the working of the monsoon continues to be not fully understood. It is partly due to the difficulties involved in getting upper air observations over the vast stretches of the seas around India.
Recent findings about the mechanism of the monsoon are based on a study of sea surface temperature of the Indian Ocean and Pacific ocean in the belt between the Tropic of Cancer and Tropic of Capricorn. The sea surface temperature influences air pressure and winds. The vertical ascent of air over the equatorial region is also influenced by changing sea surface temperature during the different seasons.
The phenomenon called the “Southern Oscillation” noted by sir Gilbert Walker postulates a sea-saw pattern of weather between the Pacific Ocean and Indian Ocean extending from Australia to Africa. When the pressures tended to be high over the Pacific Ocean, it tended to be low over the Indian Ocean. When low pressures prevail over the Indian Ocean in winter months, the chances are the succeeding summer monsoon will be good in terms of rainfall. The Southern Oscillation has a period of two to five years.
The Southern Oscillation is also known as the Walker cell, which is a east-west circulation in upper air. The air which rises over Indonesia represents the ascending branch of Walker cell. The descending branch is located over the semi-arid regions of north-west India, Pakistan and the Middle East.
There is another Walker cell between Indonesia and eastern Pacific along the west coast of South America where upwelling of cold water takes place. The difference in sea surface temperature between Indonesia (warm) and east Pacific (cold) provides the driving force for the Walker cell. At times, when the sea surface temperature between these two regions is not much, the circulation around the Walker cell weakens. The ocean current off the west coast of South America becomes warmer owing to reduced upwelling of sea water. This relatively warm current off the west coast of South America becomes warmer owing to reduced upwelling of sea water. This relatively warm current near the coast is called El Nino. This phenomenon occurs once in two to five years. The occurrence of El Nino in the eastern Pacific coincides with poor monsoon over India.
Another upper air circulation which has influence on the monsoon is the Hadley cell which represents a north-south movement. The plateau of Tibet is unusually warm is summer and acts as an elevated heat source. The ascending air above the source gradually spreads southwards to join a descending limb over the north Indian Ocean near the Mascarnes High. The south-westerly monsoon winds at the surface form the return current to complete the Hadley cell.
Thus the mechanism of the monsoon is influenced by the circulation of air over North-South cell called Hadley cell and two East-West Walker cells described above. But still the vagaries of the monsoon are not yet fully unravelled.
The Indian Ocean Dipole(IOD) also known as the Indian Nino is an irregular oscillation of sea-surface temperatures in which the western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean.
The Indian Ocean Dipole (IOD) is defined by the difference in sea surface temperature between two areas (or poles, hence a dipole) – a western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia.
The IOD affects the climate of Australia and other countries that surround the Indian Ocean Basin, and is a significant contributor to rainfall variability in this region.
Like ENSO, the change in temperature gradients across the Indian Ocean results in changes in the preferred regions of rising and descending moisture and air.
In scientific terms, the IOD is a coupled ocean and atmosphere phenomenon, similar to ENSO but in the equatorial Indian Ocean.
It is thought that the IOD has a link with ENSO events through an extension of the Walker Circulation to the west and associated Indonesian throughflow (the flow of warm tropical ocean water from the Pacific into the Indian Ocean).
When the IOD and ENSO are in phase the impacts of El Niño and La Niña events are often most extreme over Australia, while when they are out of phase the impacts of El Niño and La Niña events can be diminished.
Positive event
Cooler sea surface temperatures in the western Indian Ocean relative to the east
Winds become more westerly, bringing increased cloudiness to Australia’s northwest
More rainfall in the Top End and southern Australia
A polar vortex (also known as an Arctic cyclone, sub-polar cyclone, and a circumpolar whirl) is a persistent, large-scale cyclone located near one or both of a planet’s geographical poles.
On Earth, the polar vortices are located in the middle and upper troposphere and the stratosphere. They surround the polar highs and lie in the wake of the polar front.
These cold-core low-pressure areas strengthen in the winter and weaken in the summer.
They usually span 1,000–2,000 kilometers, in which the air is circulating in a counter-clockwise fashion (in the northern hemisphere).
As with other cyclones, their rotation is caused by the Coriolis effect.
The Arctic vortex in the Northern Hemisphere has two centres, one near Baffin Island and the other over northeast Siberia.
In the southern hemisphere, it tends to be located near the edge of the Ross Ice Shelf near 160 west longitude.
When the polar vortex is strong, the Westerlies increase in strength.
When the polar cyclone is weak, the general flow pattern across mid-latitudes buckles and significant cold outbreaks occur.
Ozone depletion occurs within the polar vortex, particularly over the Southern Hemisphere, which reaches a maximum in the spring.
It is characterized by the following different seasons:
i) The Cold Season (December to February)
ii) The Hot Season (March to mid-June)
iii) The Rainy Season or the Season of the Advancing Monsoon (June to September).
iv) The Season of the Retreating Monsoon (October to November).
Position of the sun: vertically between the Equator & the Tropic of Capricorn. The Winter Season begins to set in by about the middle of October when sun’s rays do not fall vertically on any part of the sub-continent.
Temperature : Due to latitude, temperature in general decreases from south to North.
The average temperature is below 21oC& is very low at high altitudes of the North where snow falls. January is the coldest month.
Weather Conditions: clear skies, fine cool weather, low humidity & light northerly winds.
Pressure: High pressure develops over central Asia & due to the presence of the Himalayas, a subsidiary High Pressure area develops over the plain in the North-West. The sea is relatively warm and is a region of low pressure.
Winds: blow from the High Pressure area over the land to the Low Pressure area over the sea in a general North-East direction. These are off shore winds & normally do not bring rain as they blow from the land. Over the Bay of Bengal these winds pick up moisture & blow towards Tamil Nadu causing rains along the eastern coast. These winds are weak & variable.
Rainfall
Due to the apparent movement of the sun northwards, vertical rays advance towards the Tropic of Cancer.
Temperature: The belt of maximum temperature moves northward during March & April from the southern parts of the peninsula towards the northern plains.
Pressure: A strong pressure gradient is formed from the sub-tropical high pressure belt in the Indian Ocean, south of the equator to the low pressure trough over the Northern plains.
Weather conditions: dry and excessive heat.
Rainfall: The hot weather season over north India is generally dry but not without rain. The locally formed dust storms bring variable amount of convectional rainfall to different parts of the country.
By June the low pressure depression intensifies in the north-western part of the sub-continent. This depression attracts masses of moist air from the High Pressure over the Southern Indian Ocean & Arabian Sea. These strong on shore winds are the South-West Monsoons.
The South-West monsoon is normally divided into the following two currents :-
(a) The Arabian Sea current; and
(b) The Bay of Bengal current.
This current originates in the Arabian Sea and hence its name. It divides itself into following three sub currents on reaching the western coast of India.
The first current strikes against the Western Ghats & cause heavy rain of more than 250 cms on the western slopes of the Western Ghats as well as West Coastal Plain. After crossing the Western Ghats, they enter the rain shadow area of the southern plateau & cause little rainfall.
The second current enters the Narmada-Tapti trough and goes uninterrupted in the absence of any major barrier. It brings about 60 cm rainfall to Nagpur. The third current moves towards north east in a direction parallel to the Aravalis Hills. This current causes very little rainfall in whole of the Thar Desert of Rajasthan because Aravaliis are low and parallel to the direction of currents. This current causes sufficient rainfall on reaching the Himalayan region.
This divides itself into two sub-currents. The first current enters the Garo, Khasi and Jaintia Hills of Meghalaya after crossing the Ganga Delta. Here the moisture-laden monsoon winds have to take a sudden rise in the funnel-shaped hills and cause very heavy rain-fall. Mawsynram in Meghalaya receives world’s highest rainfall of 11872 mm.
The second current goes to the Himalayas and after reaching there, it moves towards the west in a direction parallel to the Himalayan ranges. The rainfall by this current is characterized by a declining trend with increasing distance from the sea.
The eastern coast of India, particularly in Tamil nadu remains relatively dry during the south-west monsoon period. This is because the Tamil Nadu coast lies in the rain-shadow area of the Arabian Sea current and is parallel to the bay of Bengal current.
An important phenomenon associated with south-west monsoon is its tendency to have ‘breaks’ or spells of dry weather. These breaks in rainfall are related to the inflow of the tropical depressions which have a fluctuating pattern. The amount as well as the intensity of the monsoon rainfall is, therefore, determined by the frequency of these depressions.
The south-west monsoon begins to retreat from the northern India by the second week of September & continue to retreat from the southern India from mid-October to the beginning of December. Unlike the ‘sudden bursts’ of the advancing monsoon, the retreat is rather gradual with the retreat of the monsoons, the clouds disappear and the sky becomes clear. The day temperatures rises slightly but the nights become pleasant with the mean minimum temperature going down to 20oC or even below that. The diurnal range of the temperature also increases. The cyclonic storms which develop in the Bay of Bengal during this season move from south-east to north-west direction and cause substantial rainfall on the eastern coast.
The Indian economy depends almost entirely on the bounty of the monsoons which bring the seasonal rains essential for agriculture, irrigation and power production. Although considerable areas of the country are provided for by irrigation from major and minor projects, nearly 60-65 percent of the cropped area still depends on the seasonal rainfall. Hydro-electric power, which is about 15 per cent of the power produced in the country for agriculture, industry and domestic use, is also dependent on such rainfall.
India has two monsoons, the south-west and the north-east. The south-west monsoon (June to September) accounts for 70 per cent of the annual rainfall. The north-east (October to December) is important only for Tamil Nadu.
The south-west monsoon blows with great regularity and its dates of onset and withdrawal have been determined with a fair degree of accuracy. It sets in along the Kerala coast by 1, June, extends to Mumbai by 10 June, and covers the whole country by the beginning of July. The north-east monsoon, an extension of the retreating monsoon, usually sets in by October. Whereas the South-west monsoon, is dependable, with almost no case of total failure being reported from any part of the country even in years of the worst drought, the north-east monsoon is less dependable and failures for several years at a stretch have led to distress from time to time.
The average annual rainfall of India is 125 cms., the highest for a land of such size anywhere in the world. But this is highly variable in space and time, with the heaviest rains occurring over the North-eastern states and along the west coast. In contrast, some districts in south-west Rajasthan receive hardly 15 cms a year. In the extreme south of the country, Kanyakumari and Tirunelveli districts get less than 30 cms. during the south-west monsoon, while heavy rains (200 cms. and more) lash the Kerala coast nearby. There are, in fact, years when the monsoon—in plentiful in the early season (June-July and fails in the late season (August - September) and vice-versa, causing concern to farmers in several parts of the country. The formation and movement of low-pressure areas, or depressions, largely determine the activity of the monsoons and account for their vagaries.
The areas of high rainfall include the west coast from Trivandum, in the south, to Mumbai in the north, receiving 200-400 cms with some localized areas in between receiving rainfall of 400-800 cms. Almost the whole of Assam, Nagaland, Meghalya, Mizoram, Arunachal Pradesh and Sikkim and parts or Manipur, Tripura and the north-eastern tip of West Bengal also receive 200 cms and more, with isolated pockets getting more then 400 cms and one unique area, Cheerapunji, as mentioned earlier, receiving nearly 900 cms of rain a year. Meghalaya and Arunachal Pradesh are the wettest parts of the country, but Assam and Kerala have the most rainfall among the bigger states. In contrast, the areas receiving rainfall of less than 40 cms a year include desert areas that extend as far south as Kachch and most of Jammu and Kashmir. Rajashtan has the least rainfall amongst the major states. Between these two extremes lies the major part of India, with rainfall receipts of 40-200 cms.
The variations in rainfall are due to two important factors the distance from the sea and the rain-shadow effect. The dominance of summer rainfall throughout almost the whole of India may be noted, followed by dry conditions that exist throughout winter.
There is a sudden increase in rainfall from May to July and a decrease during September and October the exception being Chennai, which reflects the rainfall south-eastern Andhra Pradesh and eastern Tamil Nadu get. Chennai shows a peak in October-November, mainly as a result of rainfall blown in by Bay of Bengal cyclones, while srinagar demonstrates similar conditions, but due to winter cyclones from the Mediterranean. The rainfall distribution in the interior of India is mostly controlled by the rain-shadow effect. The rainfall decreases with distance from the sea. A reverse of this occurs in the north where the rainfall decline westwards with distance from West Bengal. The topographic, or relief effect on rainfall is also seen in the distribution of rainfall, for the windward sides of the hills and mountains (Western Ghats, North-Eastern Hills and the Himalayan foothills) receive more rain than other parts of india.
The summer rains, in effect the south-west monsoon, blow up from the equator and, on reaching the southern tip of India, bifurcate into an Arabian Sea branch and Bay of Bengal branch. For the Andaman & Nicobar Islands, the onset of the monsoon is connected with the Bay of Bengal branch ; whereas for peninsular India the onset depends on the Arabian Sea branch. The Arabian Sea branch brings heavy rainfall to the coastal areas and the western slopes as it is forced to ascend over the western ghats. However, the intensity of this rainfall is conditioned by the angle of incidence the monsoon currents make with the mountains. This branch moves quickly up the west coast and reaches Goa on 5th June and Mumbai north of it, on 10th June. The Bay of Bengal branch of the monsoon moves as fast, but gets deflected by the mountains in the north-east of India and, thus, the onset of the monsoon in Kolkatta is on 8th June. By the first of July, the entire country, barring pockets in the north-west and the south-eastern coast of India, is in the grip of the monsoon. Even in years when the monsoon ‘fails’, some rain at least does fall; failure is never total during this period. The rains of summer, however, are such that there are discernible variations in the areas covered. This is linked to two factors; humidity and relief.
To a great extent, the pattern of rainfall and the pattern of humidity are the same. A low summer humidity of less than 70 per cent, effecting rainfall adversely, is found in two pockets, one along the east coast, taking in parts of Tamil Nadu and Andhra Pradesh (this stretch receives most of its rain from the north-east monsoon) and the other in the north-west, including parts of Rajasthan (the Thar Desert), Punjab and Haryana. On the other hand, wherever there are relief features in the path of the monsoon winds, the cloud-bearing winds are forced to ascend and give copious rainfall. Thus, the western slopes of the Western Ghats and the foothills of the Himalaya, most importantly in north-east India, where the Himalayan - Arakan Yona ranges make a funnel of mountains (Cherrapunji is at the mouth of the funnel), receive plenty of rain in summer.
The highest rainfall is along the west coast, in the states of Maharashtra, Karnataka and Kerala, Mangalore (in Karnataka) has the highest rainfall on the west coast during this season. North-east India (Assam, Meghalaya and Tripura) receives equally high rainfall. In fact, no part of north-eastern India gets a rainfall of less than 80 cms during the summer and the narrow zone lying in the rain-shadow of the Khasi hills in Assam, which is the only area here getting comparatively low rainfall. The rain fall is equally high in the foothills of the Himalaya. Central India, and the area around Dandakaranya, get a rainfall of more than 120 cms with isolated areas receiving rainfall of over 160 cms. Rainfall decreases westwards along the Gangetic plain and towards the south.
Along the west coast, the rainfall is high mainly due to the orographic, or relief, effect. But the rainfall decreases very sharply towards the east. The whole of the Deccan Plateau, accounting for a major part of Maharashtra, Andhra Pradesh, almost the whole of Karnataka and Tamil Nadu, experiences very low rainfall (less than 40 cms) with only a few hilly areas relieving this arid monotony with a rainfall of 80 cms. Coimbatore and the south-eastern tip of Tamil nadu, consisting of the coastal areas of the districts of Ramanathapuram and Tirunelveli, share with west Rajasthan, and Jammu and Kashmir the distinction of having the lowest rainfall in the entire country. Indian agriculture depends so much on the rainfall of the south-west monsoon that the onset and advances of summer rains make all the difference between a good year and a bad one, economically speaking.
Winter rainfall in India is due to the retreat of the south-west monsoon. This retreat is gradual across the north and west of the country, a striking contrast to the sudden burst with which it arrives. Much of September is fairly dry in the north; it is sticky and hot, with a distinct rise in temperature in many areas. Then begins a gradual cooling. By October, there may be storms related to troughs in the upper troposphere westerlies sometimes interacting violently with a trough in the retreating upper troposphere easterlies. Farther south, the rains (the north-east, or retreating, monsoon) sometimes lash down on south-eastern India in violent thunderstorms, but are more common as wider disturbances in which easterly depressions from the Bay of Bengal move across the peninsula. In absence, the winter is a reversal of the summer winds, rains and humidity, though there are marked differences in the pattern of rainfall. For instance, the north-west continues to get the lowest rainfall, being now the centre of a high-pressure area from which the winds blow towards the east, south-east and south.
The onset of the north-east monsoon in the extreme north west of India is by September, and it is in the north and west (near Delhi and Mumbai) by 1 October. The onset of this monsoon, because the retreat is gradual, lasts longer and the whole of India is, therefore, under the influence of the north-east monsoon only by 15 December Unlike the south-west monsoon winds, the north-east monsoon winds are land winds and, hence, there effect in terms of rainfall is limited. Rainfall from these winds is low over much of India, though it is higher and fairly widespread in the southern region, due to gathering moisture as it swings in from the Bay of Bengal. But ever in the south, the winter rainfall is relatively low compared to the summer rainfall in the area, except in Tamil Nadu.
The humidity at this time of the year is generally low (less than 70 per cent) in the north-west, central India and the Deccan. The lowest average, of less than 50 per cent, occurs in the Saurashtra region of Gujarat, in Himachal Pradesh and in a part of the Marathwada region of Maharashtra. Relative humidity of 50-70 per cent occurs over northern Karnataka, western Andhra Pradesh and the rest of Marathwada with this zone extending as a narrow belt across Central India up to Central Bihar and also westwards, covering most of Rajasthan. An isolated belt in this humidity range also occurs in the north covering parts of Jammu & Kashmir, Himachal Pradesh and Uttar Pradesh.
The occurrence of a zone of high humidity of more than 60 per cent along the north-western borders of India in Kashmir and Punjab is directly traceable to the influence of the Mediterranean winds. A broad belt along the coast of Tamil Nadu and Andhra Pradesh also has a humidity of more than 80 per cent during this period. The rainfall distribution in winter shows that most of India experiences drought conditions. Rajasthan for instance, gets a rainfall of as low as 2.5 cms and below. The rainfall increases towards the east and south, rainfall of 40-48 cms occurring along the east (Coromandal) coast in Tamil Nadu and in south-eastern coastal Andhra Pradesh.
The whole of the east coast, spread over the states or Tamil Nadu, Andhra Pradesh and Orissa, gets an average rainfall of over 10 cms. The highest rainfall is recorded along the coast of Thanjavur district in Tamil Nadu, a little over 80 cms. This is the main rainy season in Tamil Nadu. High rainfall is also recorded along the crest of the Western Ghats (near Indukki in Kerala). Rainfall is generally very low over parts of Madhya Pradesh, Maharashtra, Gujarat, Uttar Pradesh, Haryana and Punjab, though in the foothills of the Himalayas in northern Himachal Pradesh the rainfall is somewhat higher (20 cms). This rainfall is from the strong winds which blow into India from the Mediterranean and is very important for the cultivation of wheat in the area. Much of the east coast rainfall is from cyclones that develop during the retreating monsoon. The south-east tip of India Tamil Nadu is the only part of the country that gets rainfall in October-November, the north-east monsoon continuing to remain active. In fact, this rain comes when the north-east monsoon is most developed: that is, the north-east monsoon winds, while recurving over the Bay of Bengal, absorb a certain amount of moisture that, on reaching the southern coromadal coast, condenses to produce rain.
Of all the factors involved in the production of crops, by far the most important in India is rainfall. By comparison, the other major climatic element, temperature, is of little significance. It is, of course, a limiting factor to plant growth, especially in winter, and mainly in north India and in the hills. At the other extreme, temperature everywhere promotes high rates of evaporation during the summer and causes crop-affecting aridity. As a rule, the hottest month precedes the rains. May-June is usually the time of peak temperature, which then falls quite sharply, with the arrival of the monsoon, to a modest in July, August and September and further in the winter months. A distinctive character of the Indian climate is its three-fold division; the cool and mainly dry winter from October to February, the hot and mainly dry season from March into early June and the south-west monsoon from mid-June to September. This seasonality is as much a function of rainfall as of temperature.
The cool season, is one of general atmospheric stability. With the passing of the March equinox, the cool season is over. Temperatures rise day by day and people look forward to after noon clouds to reduce the build-up of heat and moderate the evening temperature. In April, thunder-showers bring respite and in June the monsoon bursts. With the rains comes more pleasant weather. The distribution of average annual temperature shows the general variations in temperatures in the country. Barring the mountainous Himalayan areas in the north and north-east (Meghalaya, Sikkim and Arunachal Pradesh) of the country, no part has an average temperature of less than 20oC . The average annual temperature, however, increases towards the equator. The region that has the highest average annual temperature of 27.5oC and above, including the eastern parts of Andhra Pradesh, Tamil Nadu and two small patches, one in Gujarat and the other in Orissa.
A broad belt in the north, extending from northern Rajasthan through Maharashtra and southern Madhya Pradesh and eastwards to the borders of Bangladesh, finally curving back to cover Bihar, northern Madhya Pradesh and Uttar Pradesh has a temperature average of 25o-27oC . This warm region also intrudes into the south as two prongs of a fork, the broader prong reaching through Karnataka into Andhra Pradesh and Tamil Nadu and the narrower hugging the Western Ghats and joining the broader belt at Land’s End in the South.
A marginally less warm belt, with an annual temperature average of 22.5 - 25oC , extends as the arms of a pincer, from Punjab into western Uttar Pradesh on the north and Central Madhya Pradesh and Southern Bihar in the South, gripping much of the Gangetic Plain as well. The Plateau of the Deccan also enjoys these lower average temperatures. Jammu & Kashmir, the Himalayan parts of North India, the Khasi and Jaintia hills in the north-east, and places along the crest of the Western Ghats experience temperatures that are comparatively low : 20-22.5oC . The states with the warmest year-round climates are Andhra Pradesh and Tamil Nadu, while it is coolest in Jammu & Kashmir, Himachal Pradesh and Arunachal Pradesh.
CLIMATIC REGIONS
Climates (the term refers to regions) bring together the essential elements of weather conditions that affect people, their work and their comfort; temperature, and the amount, duration and incidence of rainfall. More importantly, climates bring together those elements which are of greatest concern to the cultivators of the land. The elements of temperature and rainfall are, thus, the basis for the differences in lifestyles in different regions. Four climatic types may be distinguished for the whole or the country : Humid - those areas with more than 1000 mm of rainfall a year; sub-humid — there with between 500 and 1000 mm; Semi-arid — those with between 250 and 500 mm; and Arid — with rainfall below 250 mm a year.
Areas where average temperatures are freezing for a month or more, posing severe constraints on agriculture, are limited to the Himalaya and Kashmir. The inner regions of Kashmir, the upper Indus Valley,a and the Karakoram are distinguished from the Himalaya by their aridity; for example, in the Leh area, with its cold dry climate, the minimum temperature is below freezing from November to April, with the January maximum also below freezing point. The average rainfall is 116 mm. Altitude has an important bearing on temperature, but latitude and the equally significant topographical situation cannot be overlooked. Hill stations, Shimla and Darjeeling for instance, record an absolute minimum below freezing point, but air drainage prevents them from suffering cold for long, despite their elevation being over 2100 metres. Therefore, these places are not classified as having cold climates.
On the other hand, the length of the rainy season , during which there are two relevant regimes, one the summer rains and the other the summer drought, gives rise to some regional types that are agriculturally distinct. The extreme-east, including Arunachal Pradesh, Assam, Nagaland, Manipur and Tripura, and the windward slopes of the Ghats in Southern Kerala are all categorized under humid climate with maximum rainfall in summer. At the same time, northern coastal Tamil Nadu has a tendency towards summer drought.
The entire west coast and most of Madhya Pradesh, Orissa, Bihar, West Bengal and the eastern and Himalayan foothills of Uttar Pradesh have a humid climate with 4 - 7 wet months. Three areas constitute the region of sub - humid climate. Occupying about a third of India, the region immediately east of the Western Ghats but in the northern reaches of the peninsula receives maximum rainfall in summer, while the region in the south, in the rain-shadow, has a tendency to summer drought. A small area in north-west India receives rains in summer as well as in winter.
Semi-arid climate prevails in the south of north-west India (Rajasthan and Gujarat) while an arid climate prevails in the Thar desert. While the cultivator (in most of India) looks to the clouds for the rains which will enable him to plant his crops, the soil in which he plants them is itself a product of the interaction of climate and the materials of the land surface. The least effected by climate is the alluvium, but crops on it still depend on the rains and the surface waters impounded in the dams. Besides soil and rain there are certain features which are of local agricultural relevance. For instance, the Gangetic Plain, despite the funneling of the monsoon through the valley from the Bay of Bengal, gets less rain than the mountains and plateaus that flank it, so much so that a small area of sub-humid climate occurs in Western Bihar and Eastern Uttar Pradesh and is notorious for famines. India can be divided into six climatic regions.
i)Tropical wet climate: is characteristic of the west coast, especially in Kerala, Karnataka and Goa, where both temperature and rainfall are high.
ii)Tropical wet and dry: Climate is mainly found along much of the east coast and in the interior of the northern peninsula, with a tongue of such climate penetrating southwards into Maharashtra and Karnataka. In this region, both temperature and rainfall are important for land-related activities with rainfall perhaps more important, for temperature does not greatly alter crop rhythms.
iii) Semi-arid : There are, two patches of semi-arid areas, one in the south immediately east of the western Ghats where the rain shadow has the effect of causing drought, and the other in the north-west circling the desert, arid climate type.
iv)Humid sub-tropical : Type of climate is found in the entire Indo-Gangetic Plain which receives high rainfall. The rainfall declines towards the west where the waters from the Gangetic System make up for it. This makes it one of the most densely populated and most agriculturally worked areas of the world.
v)Humid Sub-tropical : Regions also inthe extreme north-east, where the rainfall is the highest, and in a small pocket of land with a slight rain-shadow (the Assam Valley).
vi) Highlandsstretching the length of the Indian Himalaya have cold climates but are arid. Here temperature, because of the altitudes, is the determinant of plant growth.
Floods and droughts are a manifestation of whims and fancies of the monsoon and the associated spatial and temporal variations in rainfall. Topographical, biogeographic and anthropogenic factors too play an important role.
The ultimate objective of all measures of flood control is the minimization of flood damage; this objective can be served either by flood protection works or other measures to avoid flood damage.
In the category of flood protective works may be include the following
Works primarily aimed at protection against inundation such as flood embankments, floodwalls and ring bunds. Such embankments have been in existence for centuries in India on many of the rivers in India, notably the Gandak, Damodar, Godawari, Krishna Cauvery and Kosi.
Works aimed at reducing flood peaks, such as flood control reservoirs, which hold temporarily a part of flood within the storage space provided in the reservoir so that the rate of flow below the reservoir is kept within safe limits. After the floods subside, the water is gradually released downstream. Thus peak flows in the river channel downstream of the reservoir are reduced.
Works for reduction of floods levels, such as channel improvements, cut-offs and detention basins marked reduction in flood levels along a reach can be achieved by improving the capacity of the river channel. Dredging of bars, deepening of the river bed, removal of obstructions and straightening of close loops by cut-off can be effective. Under detention basins, the flood flows are diverted into waste depressions serving as detending basins of flood ways. After the flood goes down in the main river, the water stored in the depression is permitted to flow back into the river.
Works for arresting bank erosion, namely river training works such as spurs, groynes and revetments which are scientific methods of stabilization of any portion of the river bank against attack by the river current.
Works for reduction of the rate of run-off namely watershed management, comprising flood-zoning, raising the level of habitation above the flood level; and advance flood-warning and emergency evacuation.
Surplus water is found in the basins of Brahmaputra and Barak Rivers and their tributaries cover the northeastern states, northern West Bengal, and Sikkim, Assam. In North West Bengal, the Teesta, Torsa and Jaldakha rivers frequently inundate large areas. The rivers in Manipur frequently spill over their banks.
In the Ganga basin, the flood problem is mostly in the areas on the northern bank of the Ganga River caused by the northern tributaries of Ganga. Uttar Pradesh, Bihar, and West Bengal are the worst affected states in the Ganga basin. In eastern Uttar Pradesh, the rivers that cause flooding include the Sarada, the Ghagra, the Rapti, and the Gandak besides the main Ganga River. In Haryana, flooding may take place along the Yamuna and the problem of poor drainage exists in some of the southwestern districts. In Delhi,the area along the banks of the Yamuna is flood prone. North Bihar suffers from floods almost every year due to spillage of rivers. The rivers, such as the Burhi
Gandak, the Bagmati, the Kamla and other small rivers, the Kosi in the lower reaches, and the Mahananda, spill over their banks causing considerable damage to crops and dislocation of life. High floods occur in the Ganga in some years, causing considerable inundation in Bihar ,large scale devastation takes place in Uttar Pradesh and Bihar due to high floods in the Ghaghra, the Rapti, the Gandak, the Kosi, the Mahananda, the Bagmati & Adhwara Group leading to loss of lives, dwellings, properties, installations, communication, and infrastructure facilities.. In south and central West Bengal, the Mahananda, the Bhagirathi, the Ajay,the Damodar, etc., cause flooding due to the inadequate capacity of river channels and tidal effect. In Rajasthan and Madhya Pradesh, the problem is not serious but these states have also experienced some isolated incidents of heavy floods in recent years.
Ghaggar River carries a huge quantum of flow during the monsoon period; about 150MCM of this can be utilized for recharge. Presently this water gets collected and retained in 19 natural depressions causing water logging problems in the adjoining low lying areas like Baropal, where water levels have risen from 50m below ground level to less than 5m below ground level. Judicious management of Ghaggar flood water would provide significant quantity of water for recharge.
In Orissa, damage due to floods is caused by the Mahanadi, the Brahmani and the Baitarni which have a common delta. The deltaic districts are densely populated. The small rivers of Kerala, when in high floods, occasionally cause damage. Also there is the problem of mud flow from the hills, leading to severe damages.
In the central and southern parts of the country, floods are observed in the Narmada, the Tapi, the Godavari, the Mahanadi and the Krishna. There have been instances of floods in these rivers due to very heavy rainfall in their catchments, e.g., flooding of Hoshangabad (Narmada) in 1999. The Tapi and the Narmada occasionally carry high flows which affect areas in the lower reaches in Gujarat.
The delta areas of the Mahanadi, the Godavari and the Krishna on the east coast in particular and the coastal regions of Orissa, Andhra Pradesh and Tamil Nadu in general also periodically face flood problems in the wake of cyclonic storms.
Droughts in India are caused by
Apart from immediate relief like employment relief programmes, the long-term preventive steps include.
DROUGHT PRONE REGIONS IN INDIA
Regions
Extremely affected regions:
Regions of permanent drought, these are the desert areas of the country. It includes Desert and Semi-Desert areas of Rajasthan, Kacch, Ladakh region
Severely Affected regions
It includes Malwa Plateau, Rain shadow region of Western and Eastern Ghats
Moderately Affected regions
It includes Parts of Karnataka, Maharashtra and Gujarat, Belt running through MP, Southern UP, Bihar and West Bengal, KBK districts of Orissa
The Drought-Prone Areas Programme (DPAP) was started in 1973. The objectives of the programme are: -
The programme also aims at restoration of ecological balance by harnessing, conserving and developing natural resources, i.e. land, water, vegetative cover and raising land productivity.
Statewise area of arid and semi -arid zones
State
Area (km2)
Arid
Semi-arid
Gujarat
62,180 (31.72)
90,520 (46.18)
Madhya Pradesh
-
59,470 (13.41)
Maharashtra
1,290 (0.42)
189,580 (61.61)
Rajasthan
196,150 (57.31)
121,020 (35.396)
Note: figures inside brackets represent the % of the area of the state under that category.
Drought Prone Area of India
Drought Prone Area
51.1 mha
Affected Districts
74
Affected States
13
By: Abhipedia ProfileResourcesReport error
Access to prime resources
New Courses